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Embryology > Week 2 of development > Flashcards

Week 2 of development Flashcards

1
Q

The trophoblast differentiates into ____________ (1)and _____________(2).
The embryoblast differentiates into the ___________ (3) and ___________.(4)

A
  1. Cytotrophoblast
  2. Synctiotrophoblast
  3. Epiblast
  4. Hypoblast
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2
Q

When is the bilaminar disc formed?

A

When the blastocyst implants
Day 8

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3
Q

Describe the cytotrophoblast

A

It is the inner layer
It forms mononuclear cells that migrate into the synctiotrophoblast.

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4
Q

Describe the synctiotrophoblast

A

It is the outer layer
-It is a multinuclear mass that is expanding rapidly, and as an irregular shape
-Unable to clearly view cell boundaries

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5
Q

Endometrial cells undergo ___________ to facilitate implantation

A

apoptosis

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5
Q

What regulates trophoblast fusion?

A

Cyclic Adenosine Monophosphate AMP (cyclic AMP) pathway

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6
Q

What happens to the connective tissue surrounding the implantation site?

A

Connective tissue surrounding implantation site begins to
degenerate adjacent to the synctiotrophoblast.

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7
Q

How does the blastocyst get nutrition?

A

The synctiotrophoblast engulfs the endometrial cells that died due to apoptosis. That is how it nourishes itself

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8
Q

What are lacunae?

A

Irregular spaces in the synctiotrophoblast which fuse. The fused spaces are called lacunae.

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9
Q

What is the function of the lacunae in the synctiotrophoblast?

A

The trophoblastic lacunae fuse to form an intercommunicating network which communicates with maternal capillaries (sinusoids) as the synctiotrophoblast penetrates the endometrium further.

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10
Q

Name the usual implantation site

A

Superior part of the body of the uterus
- More often on the posterior wall than the anterior wall.

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11
Q

Define ectopic pregnancy

A

Implantation outside the uterus

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12
Q

State the 4 sites of ectopic pregnancy

A

Tubal (most common) – in the uterine tubes
▪ Ovarian (least common) – at the ovary
▪ Abdominal – in the mesentry of the abdomen
▪ Cervical – sometimes included as uterine pregnancy but is considered ectopic

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13
Q

What hormone does a pregnancy test detect? and what structure releases this hormone?

A

*HCG (Human chorionic gonadotrophin) produced by synctiotrophoblast enters
maternal blood in lacunae and is the basis of pregnancy tests

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14
Q

Describe what placenta previa is.

A

Placenta previa is when the placenta partially or completely covers the opening of the cervix.
-It is caused by the implantation of the blastocyst on the inferior part of the uterus.
-This may cause bleeding due to the premature separation of the placenta during pregnancy or at the time of delivery.

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15
Q

What hormones are in the morning after pill?

A

progestins/anti-progestins - they affect implantation

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16
Q

How can intrauterine devices disturb implantation?

A

-They can cause a local inflammatory reaction to disturb implantation
- in some cases the device contains slow releasing
progesterone to disrupt endometrial development.

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17
Q

When is the bilaminar disc formed?

A

Approximately day 8

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18
Q

Describe the two layers of the bilaminar disc

A

A distinct external layer of columnar cells – EPIBLAST
▪ Adjacent to the amniotic cavity

  • An internal layer of cuboidal cells – HYPOBLAST
    ▪ Adjacent to the blastocyst cavity.
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19
Q

How is the dorsal-ventral axis of the blastocyst defined?

A

Hypoblast - ventral
Epiblast - dorsal

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20
Q

Describe amnion and amniotic cavity formation

A

Implantation progresses – fluid-filled space appears in
embryoblast
- Space is the primordium for Amniotic Cavity
* Amnioblasts separate from epiblast forming AMNION
which encloses Amniotic Cavity

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21
Q

_____________ forms floor of the amniotic cavity, and continues peripherally with amnion

A

Epiblast

22
Q

When does the formation of amniotic cavity occur?

A

Around day 8 - it forms together with the bilaminar disc.

23
Q

What forms the roof of the exocoelomic membrane?

A

Hypoblast

24
Q

What is the derivative of amnion?

A

Epiblast cells

25
Q

What lines the primary umbilical vesicle?

A

-Superiorly there is hypoblast layer.
-Inferiorly there is exocoelomic membrane.

26
Q

What forms the extraembryonic mesoderm?

A

Outer layer of cells of primary umbilical vesicle forms
EXTRAEMBRYONIC MESODERM which surrounds
primary umbilical vesicle and amnion

27
Q

How is the extraembryonic coelom formed?

A

-The extraembryonic mesoderm increases while changes in the trophoblast and endometrium occur.
-Extra embryonic coelomic spaces now form in the extraembryonic mesoderm
-Spaces fuse to form a large isolated extraembryonic coelom.

27
Q

How is the extraembryonic coelom formed?

A

-The extraembryonic mesoderm increases while changes in the trophoblast and endometrium occur.
-Extra embryonic coelomic spaces now form in the extraembryonic mesoderm
-Spaces fuse to form a large isolated extraembryonic coelom.

28
Q

what is the primordium for the chorionic cavity?

A

Extraembryonic coelom

29
Q

The primary umbilical vesicle eventually decreases in size. What causes this reduction?

A

Extraembryonic coelom formation causes primary umbilical
vesicle to decrease in size.
smaller SECONDARY UMBILICAL VESICLE forms

30
Q

What forms the secondary umbilical vesicle?

A

The cells of the hypoblast in the primary umbilical vesicle migrate as extraembryonic endodermal cells to form the secondary umbilical vesicle

31
Q

During formation of the 2ndary vesicle a large part of the ______________ is pinched off and leaves a remnant.

A

primary
vesicle

32
Q

Extraembryonic coelom splits the extraembryonic mesoderm into…? (2)

A
  1. Extraembryonic SOMATIC Mesoderm which Lines trophoblast and covers the amnion
    2.Extraembryonic SPLANCHNIC Mesoderm which Lines the umbilical vesicle
33
Q

What structures form the chorion?

A

The extraembryonic somatic mesoderm and both layers of the trophoblast.

34
Q

Name the structures that are suspended in the chorionic sac

A

Embryo
Amniotic sac
Umbilical vesicle

35
Q

Describe the primary chorionic villi

A

These villi are vascular processes of the chorion and form
columns with syncytial coverings.
- Once these cellular extensions grow into the
synctiotrophoblast they are termed primary chorionic villi

36
Q

When is the primary chorionic villi formed?

A

By the end of week 2

37
Q

How does the embryo get nutrition

A

The fluid in the lacunar spaces (embryotroph) passes to
the embryonic disc via diffusion – thus providing
nutrition to the embryo.

38
Q

How is the primordial uteroplacental circulation established?

A

The communication between the eroded endometrial
capillaries and the lacunae of the synctiotrophoblast thus
establishes the
PRIMORDIAL UTEROPLACENTAL CIRCULATION

39
Q

What carries oxygenated blood to the embryo?

A

Oxygenated blood – via Spiral Endometrial Arteries

40
Q

What carries deoxygenated blood away from the embryo?

A

Deoxygenated blood – via Endometrial veins

41
Q

When do the lacunae in the synctiotrophoblast fuse to form lacunae network?

A

~ Day 12: the adjacent lacunae have fused to form a
lacunar network

42
Q

Endometrial capillaries become___________________ to form maternal sinusoids.

A

Congested and dilated

43
Q

what is lacunar network primordial for

A

intervillous spaces of placenta

44
Q

Epiblast

A

Columnar cells
Adjacent to amniotic cavity

45
Q

Hypoblast

A

Cuboidal cells
Adjacent to blastocyst cavity

46
Q

What is the lacunar network primordial to

Around which day?

A

Intervillous spaces of placenta

12

47
Q

What allows maternal blood to flow freely to the lacunar network

A

Synctiotrophoblast erodes sinusoids

48
Q

Since the chorionic cavity is formed by extraembryonic coelom, what forms the chorion?

A

SOMATIC mesoderm

49
Q

Where is the Embryo, amniotic sac and umbilical vesicle suspended to?

A

Chorionic sac

50
Q

What suspends them to the chorionic sac?

A

Connecting stalk

51
Q

What has to be seen at the end of he second week?

A

Primary chorionic villi

Embryology (7 decks)

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